Some subsea production trees (Xmas tree), such as horizontal production trees, have a vertical bore into which operations such as wireline operations and further drilling can be undertaken. A recent technology is called through tubing rotary drilling (TTRD), for which further drilling is undertaken in an existing production well without retrieving the existing production tubing. TTRD provides significant savings, making old wells viable for further production. However, the tubing hanger comprises sealing surfaces for plugs that are inserted and activated in order to close the tubing hanger bore sealingly during production, and said sealing surfaces are vulnerable to damage during drilling operations. Said seals are metal to metal seals, and they are critical in order to avoid leakage of hydrocarbons to the environment during production.
So far no acceptable technology exists providing protection of the tubing hanger sealing surfaces, whilst providing easy testing and maintenance.
Some general bore protectors exist for use at other locations, but they are not possible to modify to function as tubing hanger bore protectors because of much larger and simpler geometry and far less demanding or very different functional requirements. Examples on existing general bore protectors are found in patent publications WO 2006103477, relating to a downhole bore protector, and U.S. Pat. No. 6,003,602A, relating to a bore protector of about 18,75″ for conventional drilling and completion. However, more relevant bore protectors are described in the patent publications US 2004/0200614 A1/U.S. Pat. Nos. 6,966,381 and 3,231,93 B1. But the solution of US 2004/0200614 A1 requires a test sleeve and do not provide sufficient protection of the vulnerable seal surfaces, and the solution of U.S. Pat. No. 3,231,93 requires a transition pipe, all of the sealing surfaces may not be protected, testing is not convenient, neither is it adapted for hanging up of a drill string.
A demand exists for a bore protector for protecting a tubing hanger bore in a production Xmas tree, and the objective of the present invention is to provide a bore protector having the required functionality.